1. Field of the Invention
The present invention relates generally to a method of forming a bearing or a shaft, and more particularly to a method of manufacturing a bearing or a shaft with hydrodynamic pressure generating grooves.
2. Description of Related Art
At present, a plurality of so-called hydrodynamic bearings have been widely used in spindle motors of electronic driving devices, such as compact disc read-only memory (CD-ROM), digital video disc (DVD), hard disks, laser beam printers, floppy disks or other heat-dissipation fans. In the electronic driving devices, it is desired to provide a hydrodynamic bearing with small size, high rotational accuracy and long life.
A typical hydrodynamic bearing comprises a bearing surface defining a bearing hole and a shaft rotatably received in the bearing hole with a bearing clearance formed between an inner circumferential surface of the bearing and an external circumferential surface of the shaft. A plurality of hydrodynamic pressure generating grooves are defined either in the inner circumferential surface of the bearing or in the external circumferential surface of the shaft. The grooves can accommodate lubricant, such as oil. During rotation of the shaft, the lubricant is driven with the rotating shaft due to the viscosity of the lubricant. A lubricating film is thus formed in the bearing clearance between the shaft and the bearing. The shaft is supported under hydrodynamic shearing stress and dynamic pressure generated by the lubricating film. The hydrodynamic bearing has low abrasion as well as long life and low extent of noise because of no radial contact between the shaft and the bearing under hydrodynamic action.
A related method of manufacturing a hydrodynamic bearing 50 showed in FIG. 1 comprises following processes of: (a1) manufacturing a bearing 52 with a bearing hole 54 therein; and (a2) defining a plurality of hydrodynamic pressure generating grooves 56 in a bearing surface 55 of the bearing 52 by means of chemical etching, electrolysis electric discharge or machining. However, the small size of the hydrodynamic bearing 50 results in difficulty in particular in the making of the grooves 56 in the bearing surface 55 of the bearing 52. This makes manufacturing of the hydrodynamic bearing 50 both time-consuming and expensive. Therefore, the related method is not suitable for mass-production of the hydrodynamic bearing 50.
A hydrodynamic bearing having a plurality of hydrodynamic pressure generating grooves defined in an inner surface thereof has been proposed (see US Patent Pub No. US 2006/0051003 A1). Each of the grooves is wedge-shaped in cross section and extends to sides of the bearing in an axial direction. During rotation of the shaft, the lubricant may leak through the sides of the bearing. As a result, the hydrodynamic action of the bearing is weakened. US No. 2006/0002640 A1 discloses a method for manufacturing a composite hydrodynamic bearing. The composite bearing is formed by combining a plurality of bearing blocks. Because the bearing blocks are manufactured separately, the composite bearing can not obtain an accurate size and concentricity. Furthermore, the lubricant is inclined to leak through interfaces between the bearing blocks. Thus the hydrodynamic action of the bearing is weakened.
It is therefore desirable to provide an improved method for mass production of a hydrodynamic bearing with good hydrodynamic properties.